1. Field of the Invention
This invention relates to an arc heater which is completely powered by alternating current.
2. Description of the Prior Art
Arc heaters of prior construction required alternating current (AC) and direct current (DC) power. The AC power was carried by the arc heater tubes or electrodes, for generating and maintaining an arc extending between the electrodes. The DC power energized field coils surrounding the tubular electrodes to provide a magnetic field around the electrodes. The DC coil current resulted in a DC magnetic field which is mainly oriented along the axis of the tubular electrodes. The interaction of the axial field with the radial current component resulted in rapid rotational arc movement (about 1,000 cycles/second). Such rapid arc movement leads to an extended electrode life and a more effective heat exhange between the high temperature arc and the cold gas to be heated. However, the DC field does not provide equal heating over both 1/2 cycles of the AC arc current. Moreover, gas is preferably admitted tangentially between the upstream and downstream electrodes so that under DC field conditions, the arc moved with and against the rotational direction of the entering gas. That condition was mainly responsible for the polarity-dependent heating and/or voltage characteristics of arc heaters of prior construction.